Multiplex pulse-width modulation power converter

ABSTRACT

A multiple pulse-width modulation power conversion device for variable-speed drive of a three-phase AC motor comprises three units (11 1 , 11 2 , and 11 3 ), each unit including n (n≧2) batteries (12 11 , 12 12 , and 12 13 ), each made up of a DC power supply or at least one battery cell, and n power converters (13 11 , 13 12 , and 13 13 ) for converting the DC power of each of these batteries to single-phase AC power. Single-phase AC terminals within each unit are connected in series, and of the single-phase AC terminals within each unit, one of the single-phase AC terminals that is not connected to the single-phase AC terminal of another power converter is connected to a star connection, and the other is connected to a respective one of three input terminals of a three-phase AC motor. The power conversion device further comprises control circuits (14 11 , 14 12 , . . . , 14 33 ) for controlling the power converters such that the AC outputs applied to the single-phase AC terminals of the n power converters within each unit are of the same phase, and further, for effecting multiple pulse-width modulation such that the AC outputs from the three units are separated by an electrical angle of 120°.

TECHNICAL FIELD

The present invention relates to a power conversion device for anelectric vehicle utilizing a battery as a main power supply.

BACKGROUND ART

Power conversion devices for electric vehicles have hitherto required ahigh-voltage battery as a power supply.

FIG. 1 is a circuit diagram showing a conventional inverter for anelectric vehicle. Inverter 502 converts the DC power from battery 503 tothree-phase AC power by typically using semiconductor switches 601-606as shown in FIG. 1 to drive AC motor 501. In this inverter 502, themaximum voltage that can be applied to AC motor 501 as interphasevoltage is equal to the battery voltage due to the connections ofsemiconductor switches 601-606. A relatively inexpensive 200 V motor istypically used as AC motor 501. A DC voltage higher than 282 V(≈200×2^(1/2)), which is the amplitude of AC 200 V, is thereforerequired as the minimum input voltage of inverter 502 in order to obtainthree-phase 200 V AC power as an AC output from inverter 502. A batteryhaving a voltage of approximately 300 V is thus necessary to drive the200-V motor.

To produce high voltage in a battery, however, 110 to 190 batteries eachhaving cells of several volts each must be connected in series. Aadditionally, to charge a large number of batteries connected in series,a high-voltage direct-current voltage higher than that of the batteriesmust be produced by means of a charger. When charging a battery in whicha large number of cells are connected in series, moreover, the voltagesof each of the cells cannot be completely equalized due to theindividual differences between the characteristics of each of the cells,and thereby causing variations in the charging conditions of each cell.The number of serial connections in the battery should therefore bereduced to a minimum to lower the charge voltage. Lowering the batteryvoltage however results in insufficient direct-current voltage for theAC motor.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a multiplepulse-width modulation power conversion device for variable-speed driveof a three-phase AC motor that accommodates the use of a low-voltagebattery.

A first multiple pulse-width modulation power conversion device of thisinvention comprises:

three units, each unit including n (n≧2) batteries each made up of a DCpower supply or at least one battery cell, n power converters forconverting the DC power of each of the batteries to single-phase ACpower, and n residual capacitance detectors for detecting the residualcapacitance of the batteries;

wherein single-phase AC terminals within each unit are connected inseries, and of the single-phase AC terminals within each unit, one ofthe single-phase AC terminals that is not connected to a single-phaseterminal of another power converter is connected to a star connection,and the other single-phase AC terminal that is not connected isconnected to a respective one of three input terminals of a three-phaseAC motor;

the first multiple pulse-width modulation power conversion devicefurther comprises control circuits for controlling said power converterssuch that AC outputs applied to single-phase AC terminals of the n powerconverters within each unit are of the same phase, and moreover, foreffecting multiple pulse-width modulation such that AC outputs from thethree units are separated by an electrical angle of 120°, and

each unit further comprises means for determining the ratio offundamental wave amplitude of AC voltage from the n power convertersconnected in series, based on the residual capacitance detected by eachof the residual capacitance detectors.

When driving a three-phase AC motor at variable speeds using the powerconversion device of the above-described construction, the outputcurrent and output voltage have a low-skew waveform because waveformcontrol is effected by multiple pulse-width modulation, and in addition,power supply and regeneration are facilitated because conversion from DCto AC is a direct conversion. Further, this embodiment facilitatesdriving an AC motor by a low-voltage battery and allows incorporation ofa battery charging capability to the power conversion device.

The invention thus enables use of voltage of a low-voltage battery,thereby increasing safety, improving charging efficiency. In addition,radio noise can also be reduced because the use of the multiplex systemallows the switching frequency of the single-phase PWM inverters to besuppressed to a low level.

Determining the ratio of the fundamental wave amplitude of the outputvoltage from the single-phase power converters connected in series,based on the residual capacitance of the batteries enables bothefficient driving of a three-phase AC motor and efficient charging ofbatteries even in cases in which the residual capacitance of each of thebatteries differs.

A second multiple pulse-width modulation power conversion device of thisinvention comprises:

three units, each unit including n batteries (n≧2) each made up of a DCpower supply or at least one battery cell, and n power converters forconverting the DC power of each of the batteries to single-phase ACpower;

wherein single-phase AC terminals within each unit are connected inseries, and of the single-phase AC terminals within each unit, one ofthe single-phase AC terminals that is not connected to a single-phaseterminal of another power converter is connected to a star connection,and the other single-phase AC terminal that is not connected isconnected to a respective one of three input terminals of a three-phaseAC motor;

the second multiple pulse-width modulation power conversion devicefurther comprises control circuits for controlling said power converterssuch that AC outputs applied to single-phase AC terminals of the n powerconverters within each unit are of the same phase, and moreover, foreffecting multiple pulse-width modulation such that AC outputs from thethree units are separated by an electrical angle of 120°, and

wherein a charging power supply and an ON/OFF switch are connected inseries between the star connection point of single-phase AC terminals ofthe three units and the neutral point of the winding of the three-phaseAC motor; and after turning on the ON/OFF switch, switching of theconductive states of switch elements in each power converter causesindividual charging or batch charging of the batteries of that powerconverter.

In this case, after switching on the ON/OFF switch, switching theconductive states of the switch elements in a power converter causesindividual charging or batch charging of the batteries of that powerconverter.

A third multiple pulse-width modulation power conversion device of thisinvention comprises:

a battery made up of a DC power supply or at least one battery cell; and

three units, each unit including n (n≧2) first power converters forconverting DC power of the battery to AC power, n transformers forinsulating output from each first power converter, and n second powerconverters for converting power from each transformer to single-phase ACpower;

wherein the single-phase AC terminals within each unit are connected inseries, and of the single-phase AC terminals within each unit, one ofthe single-phase AC terminals that are not connected to the single-phaseAC terminal of another second power converter is connected to a starconnection, and the other single-phase AC terminal that is not connectedis connected to a respective one of the three input terminals of thethree-phase AC motor;

and the third multiple pulse-width modulation power conversion devicefurther comprises control circuits for controlling the second powerconverters such that AC outputs applied to single-phase AC terminals ofthe n second power converters within each unit are of the same phase,and moreover, for effecting multiple pulse-width modulation such that ACoutputs from the three units are separated by an electrical angle of120°;

wherein a charging power supply and an ON/OFF switch are connected inseries between the star connection point of single-phase AC terminals ofthe three units and the neutral point of the winding of the three-phaseAC motor; and after turning on the ON/OFF switch, switching of theconductive states of switch elements of each power converter causesindividual charging or batch charging of the batteries of that powerconverter.

When driving a three-phase AC motor at variable speeds using the powerconversion device of the above-described construction, multiplexing withone battery as the power supply is possible because multiplexing occursafter first converting the power of the battery to AC power and theninsulating by a transformer. In addition, waveform control bysingle-phase pulse-width modulation at each unit made up of a pluralityof modules provides output current and output voltage having a low-skewwaveform, and also enables easy supply and regeneration of power. Whencharging, moreover, this power conversion device allows charging of thebattery in the regeneration mode of each of the units, thus enabling theincorporation of a charging capability in the power conversion deviceitself. Finally, safety is enhanced because the input/output of eachinverter module can be made low voltage, and safety is further enhancedbecause the input and output are insulated.

A fourth multiple pulse-width modulation power conversion device of thisinvention comprises:

a battery made up of a DC power supply or at least one battery cell;

a first power converter for converting the DC power of said battery toAC power;

a transformer taking output of said first power converter asprimary-side input and having insulated output on its secondary side;and

three units, each unit including n (n≧2) second power converters forconverting insulated power from said transformer to single-phase ACpower;

wherein the single-phase AC terminals within each unit are connected inseries, and of the single-phase AC terminals within each unit, one ofthe single-phase AC terminals that is not connected to the single-phaseAC terminal of another second power converter is connected to a starconnection, and the other single-phase AC terminal that is not connectedis connected to a respective one of the three input terminals of thethree-phase AC motor;

the fourth multiple pulse-width modulation power conversion devicefurther comprises control circuits for controlling the second powerconverters such that AC outputs applied to single-phase AC terminals ofthe n second power converters within each unit are of the same phase,and moreover, for effecting multiple pulse-width modulation such that ACoutputs from the three units are separated by an electrical angle of120°;

wherein a charging power supply and an ON/OFF switch are connected inseries between the star connection point of single-phase AC terminals ofthe three units and the neutral point of the winding of the three-phaseAC motor; and after turning on the ON/OFF switch, switching of theconductive states of switch elements in each power converter causesindividual charging or batch charging of the batteries of that powerconverter.

In such a case, one battery, one first power converter, and onetransformer may be provided to each unit.

When performing variable-speed drive of a three-phase AC motor using apower conversion device of the above-described construction,multiplexing with one battery as the power supply is possible becausemultiplexing occurs after first converting the power of the battery toAC power and then insulating by a transformer. In addition, the multiplepulse-width modulation waveform control that is carried out at each ofthe three units made up of a plurality of second power convertersprovides output current and output voltage having a low-skew waveform,and also allows free and easy supply and regeneration of power. Whencharging, moreover, this power conversion device allows charging of thebattery in the regeneration mode of each of the units, thus enabling theincorporation of a charging capability in the power conversion deviceitself. Further, safety is enhanced because the input/output voltage ofeach PWM inverter can be made low voltage, and because the battery andmotor are insulated from each other. Finally, the safety of the batteryunit is improved because low-voltage batteries can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a conventional drive circuitutilizing an inverter;

FIG. 2 shows the construction of a multiple pulse-width modulation powerconversion device according to a first embodiment of the presentinvention;

FIG. 3 is a detailed circuit diagram of each of units 11₁, 11₂, and 11₃in FIG. 2;

FIG. 4 is a vector diagram showing the relation between the outputvoltages V_(u), V_(v), and V_(w) from single-phase PWM inverters 13₁₁-13₃₃ and interphase voltages V_(uv), V_(vw), and V_(wu) of three-phaseAC m or 1 in FIG. 2;

FIG. 5 is a circuit diagram of a PWM converter constituted by connectingswitch of a single-phase PWM inverter and the winding reactor of athree-phase AC motor;

FIG. 6 is a chart showing the fundamental waveforms of the outputvoltage V and AC voltages V₁, V₂, and V₃ from the single-phase PWMinverters of one unit of the power conversion device shown in FIG. 2;

FIG. 7 shows the consturction of the multiple pulse-width modulationpower conversion device according to a second embodiment of the presentinvention;

FIG. 8 is a detailed circuit diagram of one unit of the power conversiondevice shown in FIG. 7;

FIG. 9 is a chart showing the fundamental waveforms of output voltage Vand AC output voltages V₁, V₂, and V₃ from single-phase PWM inverters ofone unit of power conversion device shown in FIG. 7 when driving an ACmotor;

FIG. 10 is a chart showing the fundamental waveforms of output voltage Vand the AC output voltages V₁, V₂, and V₃ from single-phase PWMinverters of one unit of the power conversion device shown in FIG. 7during recharging;

FIG. 11 shows the structure of the multiple pulse-width modulation powerconversion device according to a third embodiment of the presentinvention;

FIG. 12 is a circuit diagram showing DC←→AC inverter 24 and AC←→ACinverter 2 of the power conversion device of FIG. 11;

FIG. 13 shows the structure of the multiple pulse-width modulation powerconversion device according to a fourth embodiment of the presentinvention;

FIG. 14 is a circuit diagram showing DC←→SAC inverter 33 and AC←→ACinverters 35₁₁ -35₃₃ of the power conversion device shown in FIG. 13;and

FIG. 15 shows the construction of the multiple pulse-width modulationpower conversion device according to a fifth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 shows a structural of the power conversion device according to afirst embodiment of the present invention. The power conversion deviceof this embodiment performs variable-speed drive of three-phase AC motor1, and comprises three units 11₁, 11₂, and 11₃.

Unit 11₁ comprises three batteries 12₁₁, 12₁₂, and 12₁₃, each made up ofone or more battery cells and single-phase PWM inverters 13₁₁, 13₁₂, and13₁₃, which are power converters that convert the DC power of each ofbatteries 12₁₁, 12₁₂, and 12₁₃ to single-phase AC power. Unit 11₂comprises three batteries 12₂₁, 12₂₂, and 12₂₃, each made up of one ormore battery cells and single-phase PWM inverters 13₂₁, 13₂₂, and 13₂₃,which are power converters that convert the DC power of each ofbatteries 12₂₁, 12₂₂, and 12₂₃ to single-phase AC power. Unit 11₃comprises three batteries 12₃₁, 12₃₂, and 12₃₃, each made up of one ormore battery cells and single-phase PWM inverters 13₃₁, 13₃₂, and 13₃₃,which are power converters that convert the DC power of each ofbatteries 12₃₁, 12₃₂, and 12₃₃ to single-phase AC power.

Single-phase AC terminal s of single-phase PWM inverter 13₁₁, isconnected to single-phase AC terminal r of single-phase PWM inverter13₁₂, and single-phase AC terminal s of single-phase PWM inverter 13₁₂is connected to single-phase AC terminal r of single-phase PWM inverter13₁₃. Single-phase AC terminal s of single-phase PWM inverter 13₂₁ isconnected to single-phase AC terminal r of single-phase PWM inverter13₂₂, and single-phase AC terminal s of single-phase PWM inverter 13₂₂is connected to single-phase AC terminal r of single-phase PWM inverter13₂₃. Single-phase AC terminal s of single-phase PWM inverter 13₃₁ isconnected to single-phase AC terminal r of single-phase PWM inverter13₃₂, and single-phase AC terminal s of single-phase PWM inverter 13₃₂is connected to single-phase AC terminal r of single-phase PWM inverter13₃₃. Each of single-phase AC terminals r of single-phase PWM inverter13₁₁, 13₂₁, and 13₃₁ are connected to input terminals u, v, and w,respectively, of three-phase AC motor 1. Each of single-phase ACterminals s of single-phase PWM inverter 13₁₃, 13₂₃, and 13₃₃ areconnected to a star connection (neutral point b).

Charging power supply 2 and switch 3, which connects charging powersupply 2 to three-phase AC motor 1 during charging of batteries 12₁₁-12₃₃, are connected in series between the neutral point a ofthree-phase AC motor 1 and neutral point b.

FIG. 3 is a circuit diagram showing the details of each of units 11₁-11₃.

Single-phase PWM inverter 13_(i1) (i=1-3) includes DC terminals P and N,single-phase AC terminals r and s, semiconductor switches 211-214,capacitor 201, and PWM generator 14_(i1), which is a control circuitthat produces a PWM waveform in accordance with output voltage commandV₁ * (=V*/3, where V* is the output voltage command of one unit), andturns on/off semiconductor switches 211, 212, 213, and 214 with signalsS11, S12, S13, and S14, respectively. Single-phase PWM inverter 13_(i2)(i=1-3) includes DC terminals P and N, single-phase AC terminals r ands, semiconductor switches 221-224, capacitor 202, and PWM generator14_(i2), which is a control circuit that produces a PWM waveform inaccordance with output voltage command V₂ * (=V*/3, where V* is theoutput voltage command of one unit), and turns on/off semiconductorswitches 221, 222, 223, and 224 with signals S21, S22, S23, and S24,respectively. Single-phase PWM inverter 13_(i3) (i=1-3) includes DCterminals P and N, single-phase AC terminals r and s, semiconductorswitches 231-234, capacitor 203, and PWM generator 14_(i3), which is acontrol circuit that produces a PWM waveform in accordance with outputvoltage command V₃ * (=V*/3, where V* is the output voltage command ofone unit), and turns on/off semiconductor switches 231, 232, 233, and234 with signals S31, S32, S33, and S34, respectively.

PWM generators 14₁₁, 14₁₂, and 14₁₃ effects control such that thefundamental wave voltages of AC outputs at single-phase AC terminals rand s of single-phase PWM inverters 13₁₁, 13₁₂, and 13₁₃ of unit 11₁ areof the same phase. Similarly, PWM generators 14₂₁ -14₂₃ and 14₃₁ -14₃₃respectively effect control such that the fundamental wave voltages ofthe AC outputs at the single-phase AC terminals r and s of single-phasePWM inverters 13₂₁, 13₂₂, and 13₂₃ of unit 11₂ and to the single-phaseAC terminals r and s of single-phase PWM inverters 13₃₁, 13₃₂, and 13₃₃of unit 11₃ are of the same phase. Multiple pulse-width modulation isthen effected such that the phases of the AC outputs of units 11₁, 11₂,and 11₃ are each separated by an electrical angle of 120°. The relationbetween the interphase voltages V_(uv), V_(vw), and V_(wu) appliedbetween the three input terminals u, v, and w of three-phase AC motor 1and the AC output voltages V_(u), V_(v), and V_(w) of each of units 11₁,11₂, and 11₃ is shown as a voltage vector chart in FIG. 4. It can beseen from FIG. 4 that the voltages V_(u), V_(v), and V_(w) necessary foreach unit 11₁ -11₃ to output should be 1/3^(1/2) the amplitude ofinterphase voltages V_(uv), V_(vw), and V_(wu). In addition, since eachunit 11₁ -11₃ is made up of three single-phase PWM inverters, themaximum value of the output voltage from each of single-phase PWMinverters 13₁₁ -13₃₃ therefore should be 1/3·3^(1/2) the amplitude ofinterphase voltages V_(uv), V_(vw), and V_(wu) of three-phase AC motor1, and the battery voltage of single-phase PWM inverters 13₁₁ -13₃₃should also be a voltage higher than 1/3·3^(1/2) the interphase voltagesV_(uv), V_(vw), and V_(wu) of three-phase AC motor 1. Batteries 12₁₁-12₃₃ may therefore be of lower voltage than those of the prior art.

When charging batteries 12₁₁ -12₃₃, the three units 11₁ -11₃ areconnected in parallel with charging power supply 2 because chargingpower supply 2 is connected to neutral points a and b through switch 3,and batteries 12₁₁ -12₃₃ are thus charged. At this time, individualcharging or charging by serial connection of each of batteries 12₁₁-12₃₃ is enabled by switching the conductive states of semiconductorswitches 211-214, 221-224, and 231-234 of each of single-phase PWMinverters 13₁₁ -13₃₃.

In addition, an AC power supply can also be used as charging powersupply 2 if the switch elements 211-214, 221-224, and 231-234 ofsingle-phase PWM inverters 13₁₁ -13₃₃ are controlled such that batteries12₁₁ -12₃₃ are charged with polarity matched to charging power supply 2.If a large reactor exists in the winding of three-phase AC motor 1,moreover, a PWM converter such as in FIG. 5 can be constructed by switchelements 211-214, 221-224, and 231-234 of single-phase PWM inverters13₁₁ -13₃₃ and winding reactor 4 of three-phase AC motor 1. Batteries12₁₁ -12₃₃ can thus be charged even if the charging power supply voltageis lower than the battery voltage because the PWM converter can boostthe power supply voltage.

A PWM generator is provided in each of single-phase PWM inverters 13₁₁-13₃₃ in this embodiment, but it is also possible to control the threesingle-phase PWM inverters by providing one PWM generator in one unit.

FIG. 6 is a waveform chart showing the fundamental waves of the outputvoltage V from one unit and the output voltages V₁, V₂, and V₃ from unitthree PWM inverters within one unit (FIG. 3) in the power conversiondevice of FIG. 2. As can be seen from FIG. 6, output voltage V from oneunit equals the sum of the fundamental waves of AC voltages V₁, V₂, andV₃ from the three single-phase PWM inverters, and the fundamental wavesof output voltages V₁, V₂, and V₃ from the three PWM inverters are allequal.

When output voltage V is controlled in this way, however, any disparityin the residual capacitance of the batteries will cause the battery withlowest residual capacitance to lose the capacity to output before theother batteries, and as a result, the batteries will lose the capacityto output even if there is sufficient residual capacitance in thebatteries overall. When charging batteries, there is also the problem ofdisparity in the charged state of each cell due to individualdifferences in cell characteristics.

FIG. 7 shows the structure of a multiple pulse-width modulation powerconversion device according to a second embodiment of the presentinvention which solves the aforementioned problems.

This embodiment comprises, in addition to the components of the powerconversion device according to the first embodiment: residualcapacitance detectors 15₁₁, 15₁₂, 15₁₃ for detecting the residualcapacitance of each of batteries 12₁₁, 12₁₂, and 12₁₃, respectively, ofunit 11₁ ; residual capacitance detectors 15₂₁, 15₂₂, 15₂₃ for detectingthe residual capacitance of each of batteries 12₂₁, 12₂₂, and 12₂₃,respectively, of unit 11₂ ; residual capacitance detectors 15₃₁, 15₃₂,15₃₃ for detecting the residual capacitance of each of batteries 12₃₁,12₃₂, and 12₃₃, respectively, of unit 11₃ ; output voltage commandcomputing element 16₁ for seeking the output voltage commands ofsingle-phase PWM inverters 13₁₁, 13₁₂, and 13₁₃ based on the residualcapacitance detected from residual capacitance detectors 15₁₁, 15₁₂, and15₁₃ and outputting to PWM generators 14₁₁, 14₁₂, and 14₁₃ ; outputvoltage command computing element 16₂ for seeking the output voltagecommands of single-phase PWM inverters 13₂₁, 13₂₂, and 13₂₃ based on theresidual capacitance detected from residual capacitance detectors 15₂₁,15₂₂, and 15₂₃ and outputting to PWM generators 14₂₁, 14₂₂, and 14₂₃ ;and output voltage command computing element 16₃ for seeking the outputvoltage commands of single-phase PWM inverters 13₃₁, 13₃₂, and 13₃₃based on the residual capacitance detected from residual capacitancedetectors 15₃₁, 15₃₂, and 15₃₃ and outputting to PWM generators 14₃₁,14₃₂, and 14₃₃.

FIG. 8 is a circuit diagram showing the details of each of units 11₁-11₃. If the output voltage command value for one unit is V* and theoutput voltage command values for single-phase PWM inverters 13_(i1),13_(i2), 13_(i3) (i=1-3) are V₁ *, V₂ *, and V₃ *, respectively; then,when driving three-phase AC motor 1, the output voltage commandcalculator 16_(i) (i=1-3) calculates the output voltage commands V₁ *,V₂ *, and V₃ * for single-phase PWM inverters 13_(i1), 13_(i2), and13_(i3) from the output voltage command V* for one unit and the residualcapacitance Q₁, Q₂, and Q₃ of batteries 12_(i1), 12_(i2), and 12_(i3)each detected at residual capacitance detectors 15_(i1), 15_(i2), and15_(i3) using the following equations (1), (2), and (3):

    V.sub.1 *={Q.sub.1 /(Q.sub.1 +Q.sub.2 +Q.sub.3)}×V*  (1)

    V.sub.2 *={Q.sub.2 /(Q.sub.1 +Q.sub.2 +Q.sub.3)}×V*  (2)

    V.sub.3 *={Q.sub.3 /(Q.sub.1 +Q.sub.2 +Q.sub.3)}×V*  (3)

and applies V₁ *, V₂ * and V₃ * to PWM generators 14_(i1), 14_(i2), and14_(i3), respectively. PWM generators 14_(i1), 14_(i2), and 14_(i3)produce PWM waveforms in accordance with these output voltage commandsV₁ *, V₂ *, and V₃ * and turn on/off semiconductor switches 211-214,221-224, and 231-234.

For example, when Q₁ =80%, Q₂ =50%, and Q₃ =20%, V₁ *=0.53V*, V₂*=0.33V*, and V₃ *=0.13V*. FIG. 9 shows the fundamental wave of theoutput voltage V from one unit and the fundamental waves of the outputvoltages V₁, V₂, and V₃ from each of the single-phase PWM inverters atthis time.

When charging, output voltage command calculator 16_(i) (i=1-3)calculates the output voltage commands V₁ *, V₂ *, and V₃ * for ofsingle-phase PWM inverters 13_(i1), 13_(i2), and 13_(i3) from the outputvoltage command V* for one unit and the residual capacitance Q₁, Q₂, andQ₃ of batteries 12_(i1), 12_(i2), and 12_(i3) each detected by residualcapacitance detectors 15_(i1), 15_(i2), and 15_(i3) using the followingequations (4), (5), and (6):

    V.sub.1 * ={(1-Q.sub.1)/(1-(Q.sub.1 +Q.sub.2 +Q.sub.3))}×V*(4)

    V.sub.2 * ={(1-Q.sub.2)/(1-(Q.sub.1 +Q.sub.2 +Q.sub.3))}×V*(5)

    V.sub.3 * ={(1-Q.sub.3)/(1-(Q.sub.1 +Q.sub.2 +Q.sub.3))}×V*(6)

and applies V₁ *, V₂ * & V₃ * to PWM generators 14_(i1), 14_(i2),14_(i3), respectively. PWM generators 14_(i1), 14_(i2), and 14_(i3)produce PWM waveform from these output voltage commands V₁ *, V₂ *, andV₃ * and turn on/off semiconductor switches 211-214, 221-224, and231-234.

For example, when Q₁ =80%, Q₂ =50%, and Q₃ =20%, V₁ *=0.13V*, V₂*=0.33V*, and V₃ *=0.53V*. FIG. 10 shows the fundamental wave of outputvoltage V from one unit and the fundamental waves of the output voltagesV₁, V₂, and V₃ from each single-phase PWM inverter at this time.

This embodiment allows three-phase AC motor 1 to be effectively drivenand the batteries to be effectively charged even when the residualcapacitance of each of the batteries differs.

FIG. 11 shows the structure of the multiple pulse-width modulation powerconversion device according to a third embodiment of the presentinvention.

The power conversion device of this embodiment comprises battery 22 madeup of at least one battery cell, and three units 21₁, 21₂, and 21₃.

Unit 21₁ consists of three inverter modules 23₁₁, 23₁₂, and 23₁₃, unit21₂ consists of three inverter modules 23₂₁, 23₂₂, and 23₂₃, and unit21₃ consists of three inverter modules 23₃₁, 23₃₂, and 23₃₃.

Inverter modules 23₁₁, 23₁₂, . . . , 23₃₃ are all of the sameconstruction, each consisting of DC terminals P and N, DC←→AC inverter24, insulating transformer 25, AC←→AC inverter 26, and single-phase ACterminals r and s. PWM generators 27₁₁, 27₁₂, . . . , 27₃₃ are added toinverter modules 23₁₁, 23₁₂, . . . , 23₃₃, respectively.

FIG. 12 is a circuit diagram showing DC←→AC inverter 24 and AC←→ACinverter 26.

DC←→AC inverter 24 consists of capacitor 301 and semiconductor switches311-314, and AC←→AC inverter 26 consists of capacitor 302 andsemiconductor switches 315-322, both inverters being capable ofregeneration.

Single-phase AC terminal s of inverter module 23₁₁ is connected tosingle-phase AC terminal r of inverter module 23₁₂, and single-phase ACterminal s of inverter module 23₁₂ is connected to single-phase ACterminal r of inverter module 23₁₃. Single-phase AC terminal s ofinverter module 23₂₁ is connected to single-phase AC terminal r ofinverter module 23₂₂, and single-phase AC terminal s of inverter module23₂₂ is connected to single-phase AC terminal r of inverter module 23₂₃.Single-phase AC terminal s of inverter module 23₃₁ is connected tosingle-phase AC terminal r of inverter module 23₃₂, and single-phase ACterminal s of inverter module 23₃₂ is connected to single-phase ACterminal r of inverter module 23₃₃. The single-phase AC terminals r ofeach of inverter modules 23₁₁, 23₂₁, and 23₃₁ are connected to inputterminals u, v, and w, respectively, of three-phase AC motor 1.Single-phase AC terminals s of inverter modules 23₁₃, 23₂₃, and 23₃₃ areconnected in a star configuration (neutral point b).

Charging power supply 2 and switch 3, which connects charging powersupply 2 to three-phase AC motor 1 when charging battery 22, areprovided between neutral point b and neutral point a of three-phase ACmotor 1.

The three inverter modules within each of units 21₁, 21₂, and 21₃ arecontrolled by the PWM generator such that the fundamental wave voltagesof AC outputs applied to single-phase AC terminals r and s are all thesame phase. Furthermore, the three inverter modules are controlled withmultiple pulse-width modulation by means of the PWM generators togenerate AC outputs such that the fundamental wave voltages from thethree units 21₁, 21₂, and 21₃ are separated by an electrical angle of120° to drive three-phase AC motor 1. The relation between interphasevoltages V_(uv), V_(vw), and V_(wu) and the AC output voltages V_(u),V_(v), and V_(w) of each of units 21₁, 21₂, and 21₃ applied between thethree input terminals u, v, and w of three-phase AC motor 1 is shown asa voltage vector chart in FIG. 4. From FIG. 4, it can be seen that thevoltages V_(u), V_(v), and V_(w) necessary for each of units 21₁ -21₃ tooutput should be 1/3^(1/3) the amplitude of interphase voltages V_(uv),V_(vw), and V_(wu), respectively. In addition, since each of units 21₁-21₃ consists of three inverter modules, the maximum output voltage fromeach of inverter modules 23₁₁ -23₃₃ should be 1/3.sup.·31/2 theamplitude of interphase voltages V_(uv), V_(vw), and V_(wu) ofthree-phase AC motor 1, and the battery voltage of inverter modules 23₁₁-23₃₃ should also be a voltage higher than 1/3·3^(1/2) the interphasevoltages V_(uv), V_(vw), and V_(wu) of three-phase AC motor 1.Semiconductor switches 311-322 of inverter modules 23₁₁ -23₃₃ cantherefore be for lower voltage than in the prior art.

Since output terminals r and s of inverter modules 23₁₁ -23₃₃ areinsulated from input terminals P and N, the inputs to each of invertermodules 23₁₁ -23₃₃ can be taken from one battery 22. In addition, sincetransformer 25 is incorporated within inverter modules 23₁₁ -23₃₃, thevalues of input voltage and output voltage can be freely determined atthe design stage by changing the turn ratio of transformer 25. Inaddition, the input voltage to AC←→AC inverter 26 can be freely variedif a configuration is adopted in which a step-up/step-down converter iscontrolled by DC←→AC inverter 24 and transformer 25. Further, raisingthe frequency of AC power passing through transformer 25 allows the useof a compact transformer as transformer 25. Inverter modules 23₁₁ -2₃₃need only accommodate capacitance in which the overall output is dividedby the number of inverter modules (in this case, nine), and each ofinverter modules 23₁₁ -23₃₃ can therefore be miniaturized.

When charging, the three units 21₁, 21₂, and 21₃ are connected inparallel with charging power supply 2 when AC or DC charging powersupply 2 is connected to neutral points a and b by way of switch 3.Battery 22 can then be charged if regeneration control is performed suchthat the power of one or a plurality of inverter modules flows from ACterminals r and s to DC terminals P and N.

FIG. 13 shows the structure of a power conversion device employingmultiple pulse-width modulation according to a fourth embodiment of thepresent invention.

The power conversion device of this embodiment consists of battery 32made up of at least one battery cell; DC←→AC inverter 33 for convertingthe DC power of battery 32 to AC power; transformer 34 that takes theoutput of DC←→AC inverter 33 as primary side input and that hasinsulated output on the secondary side; and units 31₁, 31₂, and 31₃ madeup of three AC←→AC inverters 35₁₁, 35₁₂, and 35₁₃, three AC←→ACinverters 35₂₁, 35₂₂, and 35₂₃, and three AC←→AC inverters 35₃₁, 35₃₂,and 35₃₃, that convert insulated power from transformer 34 tosingle-phase AC power. PWM generators 36₁₁, 36₁₂, . . . , 36₃₃ are addedto AC←→AC inverters 35₁₁, 35₁₂, . . . , 35₃₃, respectively.

FIG. 14 is a circuit diagram showing DC←→AC inverter 33 and AC←→ACinverters 35₁₁ -35₃₃.

DC←→AC inverter 33 is made up of capacitor 401 and semiconductorswitches 411-414, and AC←→AC inverters 35₁₁ -35₃₃ are each made up ofcapacitor 402 and semiconductor switches 415-422.

Single-phase AC terminal s of AC←→AC inverter 35₁₁ is connected tosingle-phase AC terminal r of AC←→AC inverter 35₁₂, and single-phase ACterminal s of AC←→AC inverter 35₁₂ is connected to single-phase ACterminal r of AC←→AC inverter 35₁₃. Single-phase AC terminal s of AC←→ACinverter 35₂₁ is connected to single-phase AC terminal r of AC←→ACinverter 35₂₂, and single-phase AC terminal s of AC←→AC inverter 35₂₂ isconnected to single-phase AC terminal r of AC←→AC inverter 35₂₃.Single-phase AC terminal s of AC←→AC inverter 35₃₁ is connected tosingle-phase AC terminal r of AC←→AC inverter 35₃₂, and single-phase ACterminal s of AC←→AC inverter 35₃₂ is connected to single-phase ACterminal r of AC←→AC inverter 35₃₃. Single-phase AC terminals r of eachof AC←→AC inverters 35₁₁, 35₂₁, and 35₃₁ are connected to inputterminals u, v, and w, respectively, of three-phase AC motor 1.Single-phase AC terminals s of each of AC←→AC inverters 35₁₃, 35₂₃, and35₃₃ are connected together in a star configuration (neutral point b).

Charging power supply 2 and switch 3, which connects charging powersupply 2 to three-phase AC motor 1 during charging of battery 32, areprovided between neutral point b and neutral point a of three-phase ACmotor 1.

The three AC←→AC inverters 35₁₁ -35₁₃, 35₂₁ -35₂₃, and 35₃₁ -35₃₃ ofeach of units 31₁, 31₂, and 31₃, respectively, are each controlled byPWM generators such that the fundamental wave voltages of AC powerapplied to single-phase AC terminals r and s all have the same phase,and are controlled with multiple pulse-width modulation by the PWMgenerators so as to generate AC output in which the fundamental wavevoltages from the three units 31₁, 31₂, and 31₃ are each separated by anelectrical angle of 120°, and three-phase AC motor 1 is driven. FIG. 4shows the relation between interphase voltages V_(uv), V_(vw), andV_(wu) applied across the three input terminals u, v, and w ofthree-phase AC motor 1 and AC output voltages V_(u), V_(v), and V_(w) ofeach of units 31₁, 31₂, and 31₃. As can be seen from FIG. 4, thevoltages V_(u), V_(v), and V_(w) necessary for each of units 31¹ -31³ tooutput should be 1/3^(1/2) the amplitude of interphase voltages V_(uv),V_(vw), and V_(wu). In addition, since each of units 31₁ -31₃ includesthree AC←→AC inverters, the maximum output voltage from each of AC←→ACinverters 35₁₁ -35₃₃ should be 1/3·3^(1/2) the amplitude of interphasevoltages V_(uv), V_(vw), and V_(wu) of three-phase AC motor 1, and thebattery voltage of AC←→AC inverters 35₁₁ -35₃₃ should also be1/3·3^(1/2) of interphase voltages V_(uv), V_(vw), and V_(wu) ofthree-phase AC motor 1. Semiconductor switches 415-422 of AC←→ACinverters 35₁₁ -35₃₃ may therefore be for lower voltage than in theprior art. Moreover, the output voltage may be further increased if atriple harmonic wave is added to the sine wave voltage command for theAC←→AC PWM inverters as described in "Control Device for Three-phaseInverter" of Japanese Patent Laid-open No. 28276/88.

The power supply can be taken from one battery 32 because battery 32 andAC←→AC inverters 35₁₁ -35₃₃ are insulated. In addition, the batteryvoltage and the value of the secondary-side voltage of transformer 34can be freely determined in the design stage by merely varying the turnratio of transformer 34. If a construction is adopted in which astep-up/step-down converter is controlled by DC←→AC inverter 33 andtransformer 34, the input voltage of AC←→AC inverters 35₁₁ -35₃₃ can befreely varied. Further, increasing the frequency of the AC power thatpasses through transformer 34 enables the use of a compact transformer.The capacitance of AC←→AC inverters 35₁₁ -35₃₃ need only be sufficientto accommodate the capacitance obtained by dividing the total output bythe number of inverter modules (in this case, nine), and each of AC←→SACinverters 35₁₁ -35₃₃ can therefore be miniaturized.

When charging, the three units 31₁, 31₂, and 31₃ are connected inparallel with charging power supply 2 when AC or DC charging powersupply 2 is connected to neutral points a and b by way of switch 3.Battery 32 can be charged if the flow of the power of DC←→AC inverter 33and one or a plurality of units is controlled to regenerate at thistime.

FIG. 15 shows the structure of a power conversion device using amultiple pulse-width modulation according to a fifth embodiment of thepresent invention.

The power conversion device of this embodiment assigns battery 32,DC←→SAC inverter 33, and transformer 34 of the power conversion deviceaccording to the fourth embodiment shown in FIG. 13 to each of units31₁, 31₂, and 3₁₃, batteries 32₁, 32₂, and 32₃, DC←→AC inverters 33₁,33₂, and 33₃, and transformers 34₁, 34₂, and 34₃ being assigned to units31₁, 31₂, and 31₃, respectively. The construction of this embodiment isotherwise equivalent to that of the power conversion device according tothe fourth embodiment.

What is claimed is:
 1. A multiple pulse-width modulation powerconversion device for variable-speed drive of a three-phase AC motor,comprising:three units, each unit including n (n≧2) batteries each madeup of a DC power supply or at least one battery cell, n power convertersfor converting DC power of each of said batteries to single-phase ACpower, and n residual capacitance detectors for detecting residualcapacitance of said batteries; wherein single-phase AC terminals withineach unit are connected in series, one of the single-phase AC terminalsthat is not connected to a single-phase terminal of another powerconverter is connected to a star connection, and the other single-phaseAC terminal that is not connected is connected to a respective one ofthree input terminals of said three-phase AC motor; further comprisingcontrol circuits for controlling said power converters such that ACapplied to single-phase AC terminals of said n power converters withineach unit are of the same phase, and moreover, for effecting multiplepulse-width modulation such that AC outputs from the three units areseparated by an electrical angle of 120°, and each unit furthercomprising means for determining the ratio of fundamental wave amplitudeof AC voltages from said n power converters connected in series, basedon residual capacitance detected by each of said residual capacitancedetectors.
 2. A multiple pulse-width modulation power conversion devicefor variable-speed drive of a three-phase AC motor, comprising:threeunits, each unit including n (n≧2) batteries each made up of a DC powersupply or at least one battery cell, and n power converters forconverting DC power of each of said batteries to single-phase AC power;wherein single-phase AC terminals within each unit are connected inseries, one of the single-phase AC terminals that is not connected to asingle-phase terminal of another power converter is connected to a starconnection, and the other single-phase AC terminal that is not connectedis connected to a respective one of three input terminals of saidthree-phase AC motor; further comprising control circuits forcontrolling said power converters such that AC outputs applied tosingle-phase AC terminals of said n power converters within each unitare of the same phase, and moreover, for effecting multiple pulse-widthmodulation such that AC outputs from the three units are separated by anelectrical angle of 120°, and wherein a charging power supply and anON/OFF switch are connected in series between the star connection pointof the single-phase AC terminals of said three units and a neutral pointof winding of said three-phase AC motor; and after turning on saidON/OFF switch, switching of conductive states of switch elements in apower converter causes individual charging or batch charging ofbatteries of that power converter.
 3. A multiple pulse-width modulationpower conversion device for variable-speed drive of a three-phase ACmotor, comprising:a battery made up of a DC power supply or at least onebattery cell; and three units, each unit including n (n≧2) first powerconverters for converting DC power of said battery to AC power, ntransformers for insulating output from each first power converter, andn second power converters for converting power from each transformer tosingle-phase AC power; wherein single-phase AC terminals within eachunit are connected in series, one of the single-phase AC terminals thatare not connected to the single-phase AC terminal of another secondpower converter is connected to a star connection, and the othersingle-phase AC terminal that is not connected is connected to arespective one of three input terminals of said three-phase AC motor;and further comprising control circuits for controlling second powerconverters such that AC outputs applied to single-phase AC terminals ofn second power converters within each unit are of the same phase, andmoreover, for effecting multiple pulse-width modulation such that ACoutputs from the three units are separated by an electrical angle of120°; wherein charging power supply and an ON/OFF switch are connectedin series between the star connection point of the single-phase ACterminals of said three units and a neutral point of winding of saidthree-phase AC motor; and after turning on said ON/OFF switch, switchingof conductive states of switch elements of a power converter causesindividual charging or batch charging of batteries of that powerconverter.
 4. A multiple pulse-width modulation power conversion devicefor variable-speed drive of a three-phase AC motor, comprising:a batterymade up of a DC power supply or at least one battery cell; a first powerconverter for converting DC power of said battery to AC power; atransformer taking output of said first power converter as primary-sideinput and having insulated output on its secondary side; and threeunits, each unit including n (n≧2) second power converters forconverting insulated power from said transformer to single-phase ACpower; wherein single-phase AC terminals within each unit are connectedin series, one of the single-phase AC terminals that is not connected toa single-phase AC terminal of another second power converter isconnected to a star connection, and the other single-phase AC terminalthat is not connected is connected to a respective one of three inputterminals of said three-phase AC motor; and further comprising controlcircuits for controlling second power converters such that AC outputsapplied to single-phase AC terminals of n second power converters withineach unit are of the same phase, and moreover, for effecting multiplepulse-width modulation such that AC outputs from the three units areseparated by an electrical angle of 120°; wherein a charging powersupply and an ON/OFF switch are connected in series between the starconnection point of the single-phase AC terminals of said three unitsand a neutral point of winding of said three-phase AC motor; and afterturning on the ON/OFF switch, switching of conductive states of switchelements of a power converter causes individual charging or batchcharging of batteries of that power converter.
 5. A power conversiondevice according to claim 4 wherein one each of said battery, said firstpower converter, and said transformer are provided in each unit.